An anti-theft mechanism in which an IC (Integrated Circuit) tag is attached to a commodity to prevent the theft of commodity is introduced into more and more stores such as a supermarket, a drugstore and the like. In accordance with such a mechanism, the IC tag attached to the settled commodity is irradiated with strong electromagnetic wave and the like and is therefore destroyed, thus, a gate arranged at the exit does not react to the destroyed IC tag. On the contrary, the IC tag attached to the unsettled commodity is not destroyed, and the gate still reacts to the IC tag, thus, the gate arranged at the exit reacts to the IC tag and activates a buzzer if a customer is going to intentionally take out the unsettled commodity from the store through the gate.
However, in a case in which the IC tag can still be used because it is not completely destroyed in the settlement process, the gate reacts to the IC tag although the commodity is already settled. Further, there is also a case in which the gate reacts when the commodity settled in other store is taken into the store through the gate. In these cases, troubles are brought to the customers, and the loss of public confidence in the store may be caused.